Improve error logs for missing steps

[roryabraham]

Feature request
In https://github.com/Expensify/App we have created a system for testing our GitHub Workflows on top of this project. The problem we're encountering is that when we remove or rename steps in our GitHub Workflows, act-js produces this error:

Error: Could not find step

This error is missing some important context for which step could not be found. Adding this information will improve our ability to quickly resolve the error by updating the mocks.

[roryabraham]

Apologies for the noisy feature request. This has already been implemented in #74. I thought we were up-to-date but I was mistaken. Thanks for the project 🙇🏼